In the present specification, reference is made to the following prior art documents:    [1] R. B. Schulz, A. Ale, A. Sarantopoulos et al., “Hybrid System for Simultaneous Fluorescence and X-Ray Computed Tomography,” IEEE Transactions on Medical Imaging, vol. 29, no. 2, pp. 465-473, February, 2010;    [2] A. Ale, R. B. Schulz, A. Sarantopoulos et al., “Imaging performance of a hybrid x-ray computed tomography-fluorescence molecular tomography system using priors,” Medical Physics, vol. 37, no. 5, pp. 1976-1986, May, 2010;    [3] D. Hyde, E. L. Miller, D. H. Brooks et al., “Data Specific Spatially Varying Regularization for Multimodal Fluorescence Molecular Tomography,” IEEE Transactions on Medical Imaging, vol. 29, no. 2, pp. 365-374, February, 2010;    [4] Y. T. Lin, H. Yan, O, Nalcioglu et al., “Quantitative fluorescence tomography with functional and structural a priori information,” Applied Optics, vol. 48, no. 7, pp. 1328-1336, Mar. 1, 2009;    [5] V. Ntziachristos, “Fluorescence Molecular Imaging,” Annu. Rev. Biomed. Eng., vol. 8, pp. 1-33, 2006;    [6] G. M. Turner, G. Zacharakis, A. Soubret et al., “Complete-angle projection diffuse optical tomography by use of early photons,” Optics Letters, vol. 30, no. 4, pp. 409-411, Feb. 15, 2005;    [7] A. Sarantopoulos, G. Themelis, and V. Ntziachristos, “Imaging the Bio-Distribution of Fluorescent Probes Using Multispectral Epi-Illumination Cryoslicing Imaging,” Mol Imaging Biol, Sep. 14, 2010;    [8] M. Freyer, A. B. F. Ale, R. B. Schulz et al., “Fast automatic segmentation of anatomical structures in x-ray computed tomography images to improve fluorescence molecular tomography reconstruction,” Journal of Biomedical Optics, vol. 15, no. 3, pp. 036006, 2010;    [9] S. R. Arridge, “Optical tomography in medical imaging,” Inverse Problems, vol. 15, no. 2, pp. R41-R93, April, 1999;    [10] A. Soubret, J. Ripoll, and V. Ntziachristos, “Accuracy of fluorescent tomography in the presence of heterogeneities: Study of the normalized born ratio,” Ieee Transactions on Medical Imaging, vol. 24, no. 10, pp. 1377-1386, October, 2005;    [11] M. J. Niedre, G. M. Turner, and V. Ntziachristos, “Time-resolved imaging of optical coefficients through murine chest cavities,” Journal of Biomedical Optics, vol. 11, no. 6, pp.-, November-December, 2006;    [12] C. Paige, and M. Saunders, “LSQR: An Algorithm for Sparse Linear Equations and Sparse Least Squares,” ACM T. Math. Software, vol. 8, no. 1, 1982; and    [13] M. Paige, and C. Saunders, “Algorithm 583 LSQR: Sparse Linear Equations and Least Squares Problems,” ACM T. Math. Software, vol. 8, no. 2, 1982.
Over the past few years, an increasing amount of hybrid imaging systems has been developed motivated by the improved system quality and imaging performance that can be reached when complementary modalities are combined. The most straightforward benefit of hybrid imaging systems is the seamless co-registration of images, which facilitates the super-position of information content. Additionally, advantage can be taken of the strength of one imaging modality to resolve the weakness of the other imaging modality.
Fluorescence Molecular Tomography (=FMT) is a technique developed for three-dimensional visualization of fluorescence bio-distribution in an object. The method operates in the diffuse photon regime, i.e. it detects photons that have traveled in tissues at distances that are longer than 1 mm. X-ray Computed Tomography (=X-ray CT) is a tomographic imaging method based on the direction of high-energy radiation trough an object, providing anatomical information on the object. Diffuse Optical Tomography (=DOT) is an optical tomographic imaging method aimed at the estimation of an absorption and/or scattering map of an object.
Compared to the improvements of PET images achieved after attenuation correction, the corresponding FMT image performance improvement based on hybrid implementations is expected to be more substantial. This is because photon propagation in tissue has a stronger dependence (attenuation) on the tissue optical properties compared to high-energy photons. Therefore, the development of hybrid imaging methods employing FMT has a primary goal of improving the performance of the optical method.
Several prior art imaging systems and methods are based on reconstruction of data of one modality independent from another modality. Data obtained from two or more modality systems was combined for visualization. Fluorescence tomography system data has been used for visualization together with MRI data and X-ray data.
In Ref. [1] a system was presented that combined X-ray CT and FMT in one physical housing, leading to two accurately co-registered data sets. The anatomical information from X-ray CT was subjected to a segmentation. The anatomical segmentation was used to formulate the inversion problem, leading to the object image.
In Ref. [2] a method was presented that used the data from the system mentioned above. The anatomical information from X-ray CT was subjected to a segmentation. Optical properties were assigned to the segments in the anatomical segmentation and used for the calculation of the forward model. The anatomical segmentation was used to formulate the inversion problem, leading to the object image.
In Ref. [3] anatomical information was obtained from a reference measurement with X-ray CT. A surface extracted from FMT measurements combined to a object together with the reference anatomical dataset was subjected to a segmentation. The anatomical segmentation was used to formulate a first inversion problem. Based on the object image obtained from solving the first inversion, a second inversion was formulated, leading to a final object image. As the first inversion was based on an operator of the dimensionality of the organs, the reconstruction result in ref [3] has a limited image quality only.
In Ref. [4] an absorption map of the object was estimated using DOT principles in a first inversion based on the optical data only. The absorption map was used to create a forward model. A second inversion used the optical absorption map and a segmentation based on X-ray CT information to create an object image.
The objective of the invention is to provide an improved system for creating an object image of an object under investigation being capable of avoiding limitations and disadvantages of conventional hybrid imaging techniques. In particular, the objective of the invention is to provide an improved system for the reconstruction of a fluorescence distribution in an object that makes optimal use of the combination of fluorescence tomography with a second tomographic imaging modality.